Thermal type ink jet printing devices use heads having ejection modules which are usually made from wafers of semiconducting material with technologies similar to those employed for producing integrated and/or hybrid circuits. This means that the heating elements and relative driving circuits, together with the hydraulic, ink feeding network, can be obtained, all within extremely reduced dimensions.
This is a solution used widely to produce printheads borne by carriages which, in use, are made move transversally over the surface to be printed, all of this according to a typical, serial type printing method.
The ink jet technology is also suitable for the production of printing devices having parallel or serial-parallel type heads with printing of the entire line of a page in a single run, that is without any scanning movement of the head over the surface being printed on or with a movement that is restricted to a fraction of the line.
Solutions are known that simplify the manufacture of heads for serial printing. For example, in Italian patent application No. TO2002A000144 filed on Feb. 20, 2002 by the Applicant, ejection modules are used with resistors adjacent to an edge of greater length and terminals arranged on the opposite edge, and in which nozzles are produced on a plate fixed and hydraulically tight on the module. Advantageously, feeding for the ink of the different chambers takes place through a slot in the support, common to all the chambers and which extends parallel to the nozzles.
The printing devices with heads that operate in parallel or serial-parallel are of compact dimensions and enable printers of great simplicity and limited encumbrance height-wise to be produced. Their field of application thus extends to sectors which include, inter alia, the printing of cash slips, labelling, printing in measuring equipment and photographic printing, as described for example in patent application No. TO2001A000707, filed on 19 Jul. 2001 by the Applicant.
The manufacture of ink jet printing devices having parallel or serial-parallel heads conflicts however with the difficulty of making, with a yield sufficient to allow components to be obtained economically, chips of considerable length (>1 inch) that have zero defects. Furthermore, there is also the risk, at the conclusion of the manufacturing process, of ending up with a faulty device for the sole fact that, in a head, one only of the numerous nozzles and/or heating elements is not functioning. The scale of these problems has been such as to render the production of these devices economically very unattractive up till now.
To overcome the technological and production difficulties of the parallel or serial-parallel printing devices, one proposal has been the recourse to heads with numerous elementary ejection modules of compact dimensions, assembled in such a way as to give a disposition of nozzles aligned in a common direction as in a single module, of the same length as the printing width.
The modules are stuck side by side, with pitch between the nozzles being maintained constant. This also applies to the last nozzle and the first nozzle of two adjacent units. However, other problems arise from using this structure such as, for instance, that of the impossibility of using modules in which feeding of the ink occurs through common slots.
Also proposed have been ink jet devices with heads operating in parallel, having ejection modules and nozzles in a staggered arrangement. This, however, gives rise to a worsening of the alignment of the dots in the printing phase and a more complex logic for controlling activation of the nozzles and in the associated circuitry.